The typical self-propelled compaction roller includes a main frame or chassis that supports an engine which serves to operate drive wheels to propel the roller over the terrain. A drum frame is pivotally connected by a universal joint to the main frame and rotatably supports a compaction drum or roller. A vibratory mechanism is mounted on the drum frame and acts to vibrate the drum to aid in compaction.
A common type of vibratory mechanism includes a hydraulic motor and a weight is mounted eccentrically with respect to the output shaft of the motor. The eccentric weight generated vibratory forces throughout the 360.degree. rotation of the shaft, While the vertical vibratory forces aid in compaction, the fore and aft vibratory forces are transmitted through the machine and can cause severe wear and maintenance problems. In an attempt to isolate the vibrations from the main frame to the machine, shock mounts are utilized to connect the drum to the main frame, as well as mounting the engine on the main frame.
As a further problem, when the forces are generated throughout the 360.degree. rotation of the shaft, harmonic vibrations may be set up, which act to cancel out the vertical vibratory forces, so that the compaction forces are not maximized.
It is known to employ a separate vibratory unit or exciter for each drum in a double drum compaction roller. In a unit of this type an eccentric weight is mounted on each output shaft and the weights are arranged so that when a downward vertical vibratory force is generated by one eccentric weight, an upward vertical vibratory force is generated by the other weight. The result is that the compaction forces are generated in sequence, and the sequenced vibrations are desirable in certain applications, as in asphalt paving operations, to eliminate skip marks.
It is also known, as disclosed in U.S. Pat. No. 4,647,247, to mount eccentric weights within a compaction drum, in a manner such that the vertical vibratory forces generated by the eccentric weights will cancel, while the horizontal or fore-and-aft vibratory forces add together to provide a shearing type of action on the soil.